1. Field of the Invention
The present invention relates generally to metal working tools used to remove fasteners and more specifically to tools used to remove locking collar fasteners.
2. Description of the Related Art
A locking collar fastener system, sometimes called a frangible fastener or "HI-LOK" is used in environments of high vibration, such as on aircraft. The locking collar fastener system is used wherever a rivet can be used to join parts together.
The frangible fastener system utilizes a first piece comprising a threaded shaft on one end and an exposed retaining ring at the other end. A passage is drilled through the parts to be fastened, typically large sheets of metal, such as aircraft surfaces and boats. The threaded shaft portion of the fastener is inserted through the aligned passages to the exposed retaining ring. Often the surface of the part to be fastened is indented at the hole consistent with the retaining ring to provide a flat outer surface at the area of the retainer ring. A matching threaded locking collar is hand rotated upon the threaded portion of the shaft, then controllably torqued with a wrench. The threaded locking collar joins to a wrenching ring by a notched neck which shears from the collar at a predetermined torsional loading during the torquing. The threaded locking collar having an upset portion, usually a slightly elliptical shape provides a frictional spring lock to prevent the locking collar from untreading or loosening, even in environment of high vibration and stress. The collar remains locked to the fastener shaft even when the residual tension on the fastener is lost. Exposed on each side of the parts obscuring the passage, on one side is the outer portion of the retaining ring that may be recessed and on the other side, the almost round locking collar.
The Problem of Removal
The removal of the HI LOK and other frangible fasteners without damage to the part attached often presents a challenging problem but is needed for many useful reasons. nO the HI LOK type frangible fastener, an hexagonal opening at the end of the shaft of the locking collar fastener is sufficiently recessed in depth to receive a standard allen wrench for the purpose of retaining the shaft in position with respect to the locking collar during removal.
The removal of the locked collar from the shaft is usually difficult, but necessary for repair and maintenance of the joined parts. To accomplish this, heretofore, drilling means such as a drill bit manual, electric or air-motor are used to drill out the center of the shaft portion or a cutting means such as a hack-saw is used to cut the collar. In either case, this activity weakens the fastener. Then the parts of the collar are pried, chiseled or twisted off to expose the shaft portion of the fastener within the passage. Then a knock-out pin is used to force the shaft from the passage. The problem with this method is the time it takes to drill or cut and manipulate the collar in order to expose then remove the shaft from the passage. Furthermore, scars from the removal operations and consequential weakening to the parts surrounding the passage may create problems in refastening the parts using the same passage.
Ongoing efforts have been made to improve the means to remove these types of fasteners without causing damage. Such efforts have been addressed both to the general object of improving the manner of removal of the frangible fasteners as well as the speed that these fasteners may be removed without damage to the parts fastened. Because the frangible fasteners are designed to hold parts together under environments of extreme stress and vibration, until my invention no practical, universally adaptable tool was known to address the removal of frangible fasteners.